Today, the Plasma technology makes possible to achieve flat color panels of large size and with very limited depth without any viewing angle constraints. The size of the displays may be much larger than the classical CRT picture tubes would have ever been allowed.
Referring to the last generation of European TV, a lot of work has been made to improve its picture quality. Consequently, a new technology like the Plasma one has to provide a picture quality so good or better than the old standard TV technology. This picture quality can be decomposed in different parameters, such as:    good response fidelity of the panel: A panel having a good response fidelity ensures that only one pixel could be ON in the middle of a black screen and in addition, this panel has to perform a good homogeneity. In order to improve that, a so-called “priming” process is used which aims to excite the whole cells of the panel regularly but only during a short time. Nevertheless, since an excitation of a cell is characterized by an emission of light, the priming process will modify the level of black. Therefore, this solution has to be used parsimoniously.    good brightness of the screen: This is limited by the dead time of the panel, i.e. time in which no light is produced, comprising mostly the addressing time and the erase time.    good contrast ratio even in dark room: This is limited by the brightness of the panel combined with the black level
      (          ratio      ⁢              Brightness        blacklevel              )    .In order to improve the response fidelity, the use of the “priming” process will, at the same time, reduce the contrast ratio.
All these parameters are also completely linked together and an optimal compromise has to be chosen to provide the best picture quality at the end.
A Plasma Display Panel (PDP) utilizes a matrix array of discharge cells which could only be “ON” or “OFF”. Also unlike a CRT or LCD in which gray levels are expressed by analog control of the light emission, a PDP controls the gray level by modulating the number of light pulses per frame. For that purpose, each frame will be decomposed in sub-periods called “sub-fields”.
In order to produce these light pulses, an electrical discharge will appear in a gas called plasma and the produced UV radiation will illuminate a colored phosphor.
In standard addressing methods like the method known as ADS (Address Display Separated) all the basic cycles of a such-field period are made one after the other. In order to select which pixel should be lighted, a first selective operation called addressing (or scanning) will create a charge in the cell to be lighted. Each plasma cell can be considered as a capacitor which keeps the charge for a long time. Afterwards, a general operation called “sustain” applied during the lighting period will add charges in the cell. In the cell addressed during the first selective operation, the two charges will build up and that brings between two electrodes of the cell a firing voltage. The cell will light during the whole sustain operation of each specific sub-field.
At the end, an erase operation will remove all the stored charges to prepare the cell for new cycle.
As mentioned above, the PDP controls the gray level by modulating the number of light pulses per frame.
This time modulation will be integrated by the eye over a period corresponding to the human eye time response. In the field of video processing, a 8-bit representation of a luminance level is very common and will be taken as example used to simplify the disclosure.
In that case each level will be represented by a combination of the 8 following bits:1-2-4-8-16-32-64-128
To realize such a coding scheme with the PDP technology, the frame period will be divided in 8 lighting periods (called sub-fields), each one corresponding to one of the 8 bits. The number of light pulses for the bit “2” is the double as for the bit “1 ”, and so forth. With these 8 sub-periods, it is possible through sub-field combination, to build the 256 gray levels. The standard principle used to generate this gray modulation is based on the ADS (Address Display Separated) principle, in which all operations are performed at different time on the whole panel. For illustration, FIG. 1 represents an example of ADS principle based on an 8-bit encoding scheme with only one priming at the beginning of the frame.
Each sub-field SF1, SF2, SF3 . . . SF8 comprises an erase period, an addressing period and a sustain period as shown in detail in FIG. 2. This figure illustrates the fact that except for the addressing period, all operations are performed on the whole panel in an uniform way. The addressing operation, as already said, is a selective operation which is done line by line. The overall duration of the addressing period is commonly called addressing time and represented on the figures with Tad. On standard panels, this time is equivalent to the time used for each line (Tl) multiplied by the number of lines (N) since the addressing time Tl is the same for all lines. This principle can be seen on FIG. 3.
FIG. 3 shows that, for a given sub-field, the activation of the addressing operation for each line has the same duration Tl. Then, the complete addressing time per sub-field is computed as Tad=N×Tl where N represents the total amount of addressed lines.
Actually, the only variation which can be found in the plasma field is a variation depending on the sub-field itself. In other words, the addressing time for all lines stays the same inside one sub-field writing stage but is different from sub-field to sub-field.
The table A below gives an example of one flexible addressing found on one actual product:
TABLE ASub-fieldSub-field weightAddressing time112.2 μs222.1 μs332.0 μs451.9 μs581.9 μs6131.8 μs7191.8 μs8251.8 μs9321.7 μs10401.7 μs11491.7 μs12581.7 μs
In the example described table A, the addressing time becomes shorter when the sub-field weight increases. This is due to the fact that the more sustain a sub-field contains the better the addressing efficiency is. Therefore this addressing time can also change depending on the power management. When the APL (Average Power level) of the input picture decreases, the overall number of sustains increases and the addressing time per sub-field can be decreased as shown on table B.
TABLE BAddressingAddressingAddressingAddressingSub-fieldtimetimetimetimeSub-fieldweight(APL = 0%)(APL = 20%)(APL = 60%)(APL = 100%)112.2 μs2.2 μs2.3 μs2.4 μs222.1 μs2.2 μs2.3 μs2.4 μs332.0 μs2.1 μs2.2 μs2.3 μs451.9 μs2.1 μs2.2 μs2.3 μs581.9 μs2.0 μs2.2 μs2.3 μs6131.8 μs2.0 μs2.2 μs2.3 μs7191.8 μs1.9 μs2.1 μs2.2 μs8251.8 μs1.9 μs2.1 μs2.2 μs9321.7 μs1.9 μs2.0 μs2.1 μs10401.7 μs1.9 μs2.0 μs2.1 μs11491.7 μs1.9 μs2.0 μs2.1 μs12581.7 μs1.9 μs2.0 μs2.1 μs
Therefore, the addressing time could be described as a function of two variables Tl=ƒ(SF,APL) where SF represents the sub-field number and APL the average power level (%).
However, in any case, the addressing time of standard panel stays the same from one line to the other despite the fact that the panel is not homogeneous as well as the influence of various operation like priming, sustaining and so on.